[Talk-GB] maxspeed field - what units should we use. etc

[Paul Jaggard]

Hi

I think the principle of keeping it easy for the mapper should apply.  In
the UK, speeds are signed in mph, and most mappers will think in mph, so
let's record speeds in mph.  Anything else leads to confusion, conversions,
varying degrees of accuracy.  But to my mind, the worst result is the
inability to spot errors.

For example, a stretch of ring road near me has various speed limits at
various sections.  I could tell you it's 50mph for the first bit, 30mph at
the roundabout, then 70mph beyond.  But when I looked at it recently,
different bits were marked up with a whole jumble of numbers (including 112
on one side of the dual carriageway, 113 on the other).  Yes, I can convert
from km/h to mph and back again, but not in a quick glance.

When I map in France, I tag in km/h (just using a bare number), but in the
UK I absolutely want to tag in mph.

>From a data consumer's point of view, it's not hard to take any fields with
mph at the end and preprocessing or converting on the fly, as long as
there's consistency in using an 'mph' suffix.  Seeing as there are more bare
numbers that are obviously km/h than mph, saying a bare number in the UK
should be interpreted as mph is asking for trouble, I think.

So, I think maxspeed=30mph or maxspeed=48 should both be acceptable and
equivalent, but maxspeed=30mph preferred in the UK.  maxspeed=30 should NOT
be used.

One word of caution when looking at the tag usage in the UK - I've had
swathes of my maxspeed tagging changed from mph to km/h by users (or their
bots) in Germany and elsewhere, so beware using the current usage list as a
measure how UK mappers want to tag.

Keep it simple for the mapper and tag what's on the signs, and use an mph
suffix to avoid confusion.

Paul
(southglos)
 
-----Original Message-----
Date: Thu, 4 Jun 2009 08:45:20 +0100
From: Peter Miller <peter.miller at itoworld.com>
Subject: [Talk-GB] maxspeed field - what units should we use. etc

I have been looking at the coverage of maxspeed limit data for  
highways in the UK and we seem to have a right mix of styles.

Here is the data for bug chunk of England while avoiding including  
anything from France or Ireland (which would include km/hour figure).  
We current have over 17,000 highway ways tagged with maxspeed and also  
300 ways tagged as 'maxspeed:mph'. You will notice that for 30 miles  
per hour we have 30, 30mph, 30 mph, 48.2, 48.28,  48.280, 48.27808,  
48.28032 and 48.28.

Any suggestion on what we should recommend for the UK? I guess the USA  
should also be party to this discussion but they have far less  
population of the maxspeed field (only 70 uses in the Bay area) so  
possibly we should come to a view first.  Our options seem to be:-
maxspeed=30mph (the user should strip a trailing mph to find the value)
maxspeed=30   (leaving it for the user to realise that it is in the UK  
and therefore imperial)
maxspeed=30 mph (the user should strip the last word if it is mph  
including the space)
maxspeed:mph=30 (Easy for the user)
maxspeed=48.28 (with a defined precision) For metric use no work by  
the user, for imperial use a look-up table is required or a conversion  
and rounding